An example of how pg.connect() behaves differently, when it probably should behave the same. :)

different-pg-connect.js

var async = require('async');
var pg = require('pg');
var connString = "postgres://postgres@localhost/template1";

// attempt 1 - all ok
pg.connect(connString, function(err, client, done) {
    // this function has a .length of 3 ... therefore done is defined
    console.log('1) Connected ok');
    done();
    // pg.end();
});

// attempt 2 - not ok
async.waterfall(
    [
        function(callback) {
            pg.connect(connString, callback);
        },
        function(client, done, callback) {
            console.log('2) Connected ok');
            // done is defined (but is actually the callback)
            done();
            callback(); // bang!
        }
    ],
    function(err) {
        console.log('3');
        // pg.end();
    }
);